A novel mechanism model for producing maturation-inducing steroid in fish

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CR20bHSD has been believed to be the enzyme responsible for DHP (maturation-inducing steroid) production during oocyte maturation in fish. The present study demonstrated that CR20bHSD is not responsible for DHP production and identified a novel enzyme, termed hsd17b3like, as the genuine enzyme responsible for conversion of 17aOHP to DHP during final oocyte maturation in masu salmon. The expression pattern of the mRNA was well matched with serum DHP level. Incubated granulosa cells, just before oocyte maturation period, could convert efficiently exogenous 17aOHP to DHP as well as increasing the mRNA levels when incubated with gonadotropic preparations. These results clearly indicated that hsd17b3like is the enzyme responsible for DHP production during oocyte maturation in the masu salmon, and not CR20bHSD. The present study clearly demonstrated the molecular mechanisms underlying DHP production during oocyte maturation in the masu salmon.